Nearly one-third of flights on major U.S. airlines were late in June, delays climbed to the highest point since the government began tracking data 13 years ago and more bags were mishandled, according to fresh data reported by the U.S. Department of Transportation.

Additionally, the carriers cancelled 2.7 percent of their scheduled flights — up a full percentage point compared to the same month last year.

At least part of the explanation for the increasing delays is that demand for air travel is rising.

The government said nearly 45 percent of late flights were delayed by bad weather, up 7 percent from the same month last year. Other causes included late-arriving aircraft (more than 10 percent) and aviation system delays (more than 9 percent.)

The on-time arrival rate in June was just above 68 percent, compared with roughly 73 percent a year earlier. So far in 2007, nearly 25 percent of flights on the 20 largest carriers have arrived late, the agency said.

Data submitted by the nation's 20 largest airlines show the mishandled baggage rate jumped to 7.34 reports per 1,000 passengers, up from 5.86 in the January-to-June period one year ago.

More travelers complained about airline service, too — 1,094 complaints were fielded by passengers in June, up nearly 45 percent compared with the prior year.